Gear transmission device and image forming apparatus including the same

ABSTRACT

A gear transmission device includes a first external gear driven by a drive motor attached to a first side of a frame and a first internal gear driven by the first external gear. The first internal gear includes an outer cylinder portion, an end plate, an annular opening, and an inner cylinder portion including a shaft hole. The outer cylinder portion includes internal teeth formed on an inner circumferential surface thereof. The inner cylinder portion is formed concentrically inside the outer cylinder portion. The end plate connects the outer cylinder portion, the inner cylinder portion, and the shaft hole at one end in an axial direction. In a state in which the annular opening faces a second side of the frame opposite the first side thereof, the first external gear is inserted to the annular opening to mesh with the internal teeth of the outer cylinder portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a Continuation of U.S. application Ser. No.14/449,481, filed Aug. 1, 2014, which is a Divisional of U.S. Pat. No.8,934,815, issued Jan. 13, 2015, which claims priority pursuant to 35U.S.C. §119 to Japanese Patent Application No. 2012-242571, filed onNov. 2, 2012, in the Japan Patent Office, the entire disclosure of eachof which is hereby incorporated by reference herein.

BACKGROUND

1. Technical Field

Exemplary aspects of the present disclosure generally relate to an imageforming apparatus and a gear transmission device, and more particularlyto an image forming apparatus including the gear transmission deviceequipped with an internal gear as a first-stage driven gear driven by amotor.

2. Description of the Related Art

Generally, known gear drive assemblies that drive a target at a lowspeed and a high torque include an external gear and a first-stagedriven gear that meshes with the external gear. The external gear is agear with teeth formed on the outer surface of a cylinder or a cone, andis attached to a rotary shaft of a drive motor serving as a drivesource. The first-stage driven gear meshing with the external gear isconfigured to transmit power at a high speed and low torque. In otherwords, the external gear of the motor is designed to have a small numberof teeth (pitch circle diameter) for acceleration. By contrast, thepitch circle diameter of the first-stage gear is relatively wide toachieve a greater deceleration ratio.

However, if the number of gear teeth of the external gear of the drivemotor is reduced, an adequate contact ratio between the first-stagedriven gear and the external gear cannot be secured, thereby causingfluctuation of rotation, noise, and vibration. In order to reduce noiseand vibration, in one approach, grease is injected between gear teethmeshing with each other. However, the noise and vibration still remain.Furthermore, injecting grease for multiple times causes a higher risk ofa foreign substance getting into the mesh portion between the gearteeth, which results in noise, degradation of rotation accuracy, anddamage to the gear.

In view of the above, in order to reduce the noise and vibration,JP-H11-311302-A proposes using an internal gear as the first-stage gearmeshing with the external gear attached to the rotary shaft of the drivemotor.

In this configuration, an opposite side of the meshing side of theexternal gear is exposed to an internal space of the internal gear sothat a sound of gears meshing with each other resonates in the internalspace of the internal gear and leaks outside. Furthermore, if thedurability of the internal gear is not sufficient, the vibration causedby the gear mesh resonates with the internal gear, causing the vibrationto spread outside.

In view of the above, there is an unsolved need for a gear transmissiondevice that reliably prevents undesirable noise and vibration fromdispersing from a driven gear.

SUMMARY

In view of the foregoing, in an aspect of this disclosure, there isprovided a gear transmission device including a first frame, a drivemotor, a first external gear, and a first internal gear. The drive motorincludes a rotary shaft and is attached to a first side of the frame.The first external gear is connected to the rotary shaft of the drivemotor and projects from a second side of the frame opposite the firstside. The first internal gear is disposed near the first external gearand includes an outer cylinder portion, an inner cylinder portion, anend plate, and an annular opening. The outer cylinder portion includesinternal teeth formed on an inner circumferential surface of the outercylinder portion. The inner cylinder portion is formed concentricallyinside the outer cylinder portion and includes a shaft hole formed inthe center of the inner cylinder portion. The end plate connects theouter cylinder portion, the inner cylinder portion, and the shaft holeat one end in an axial direction of the shaft. The annular opening isformed between the outer cylinder portion and the inner cylinder portionat a side opposite the end plate. In a state in which the annularopening faces the second side of the frame, the first external gear isinserted to the annular opening to mesh with the internal teeth of theouter cylinder portion.

According to another aspect, an image forming apparatus includes animage bearing member, an intermediate transfer belt, a process unit, afixing device, a sheet conveyor roller, and the gear transmissiondevice.

The aforementioned and other aspects, features and advantages would bemore fully apparent from the following detailed description ofillustrative embodiments, the accompanying drawings and the associatedclaims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be more readily obtained as the same becomesbetter understood by reference to the following detailed description ofillustrative embodiments when considered in connection with theaccompanying drawings, wherein:

FIG. 1A is a cross-sectional view schematically illustrating a geartransmission device according to a first embodiment of the presentdisclosure;

FIG. 1B is a cross-sectional view schematically illustrating the geartransmission device along a line B-B in FIG. 1A;

FIG. 2 is a cross-sectional view schematically illustrating the geartransmission device according to a second embodiment of the presentdisclosure;

FIG. 3 is a cross-sectional view schematically illustrating the geartransmission device according to a third embodiment of the presentdisclosure;

FIG. 4 is a cross-sectional view schematically illustrating the geartransmission device according to a fourth embodiment of the presentdisclosure;

FIG. 5 is a cross-sectional view schematically illustrating the geartransmission device according to a fifth embodiment of the presentdisclosure;

FIG. 6 is a cross-sectional view schematically illustrating the geartransmission device according to a sixth embodiment of the presentdisclosure;

FIG. 7 is a cross-sectional view schematically illustrating the geartransmission device according to a seventh embodiment of the presentdisclosure;

FIG. 8 is a cross-sectional view schematically illustrating the geartransmission device according to a eighth embodiment of the presentdisclosure;

FIG. 9 is a cross-sectional view schematically illustrating the geartransmission device according to a ninth embodiment of the presentdisclosure;

FIG. 10 is a cross-sectional view schematically illustrating a geartransmission device according to a tenth embodiment of the presentdisclosure;

FIG. 11 is a cross-sectional view schematically illustrating the geartransmission device according to an eleventh embodiment of the presentdisclosure;

FIG. 12 is a cross-sectional view schematically illustrating the geartransmission device according to a twelfth embodiment of the presentdisclosure;

FIG. 13 is a cross-sectional view schematically illustrating the geartransmission device according to a thirteenth embodiment of the presentdisclosure; and

FIG. 14 is a cross-sectional view schematically illustrating an imageforming apparatus employing the gear transmission device according to anillustrative embodiment of the present invention.

DETAILED DESCRIPTION

A description is now given of illustrative embodiments of the presentinvention. It should be noted that although such terms as first, second,etc. may be used herein to describe various elements, components,regions, layers and/or sections, it should be understood that suchelements, components, regions, layers and/or sections are not limitedthereby because such terms are relative, that is, used only todistinguish one element, component, region, layer or section fromanother region, layer or section. Thus, for example, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of this disclosure.

In addition, it should be noted that the terminology used herein is forthe purpose of describing particular embodiments only and is notintended to be limiting of this disclosure. Thus, for example, as usedherein, the singular forms “a”, “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. Moreover, the terms “includes” and/or “including”, when usedin this specification, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

In describing illustrative embodiments illustrated in the drawings,specific terminology is employed for the sake of clarity. However, thedisclosure of this patent specification is not intended to be limited tothe specific terminology so selected, and it is to be understood thateach specific element includes all technical equivalents that have thesame function, operate in a similar manner, and achieve a similarresult.

In a later-described comparative example, illustrative embodiment, andalternative example, for the sake of simplicity, the same referencenumerals will be given to constituent elements such as parts andmaterials having the same functions, and redundant descriptions thereofomitted.

Typically, but not necessarily, paper is the medium from which is made asheet on which an image is to be formed. It should be noted, however,that other printable media are available in sheet form, and accordinglytheir use here is included. Thus, solely for simplicity, although thisDetailed Description section refers to paper, sheets thereof, paperfeeder, etc., it should be understood that the sheets, etc., are notlimited only to paper, but include other printable media as well.

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, andinitially with reference to FIG. 1, a description is provided of animage forming apparatus according to an aspect of this disclosure.

[Embodiment 1]

With reference to FIGS. 1A and 1B, a description is provided ofEmbodiment 1 according to an illustrative embodiment of the presentdisclosure. FIG. 1A is a cross-sectional view schematically illustratinga gear transmission device of Embodiment 1. FIG. 1B is a cross-sectionalview schematically illustrating the gear transmission device along aline B-B in FIG. 1A. As illustrated in FIG. 1A, the gear transmissiondevice includes a pair of first and second frames 20 and 21, a drivemotor 30 serving as a drive source, a seat plate 31, and so forth. Thepair of frames 20 and 21 consists of two vertical (perpendicular) platesdisposed parallel with each other. The drive motor 30 is attached to oneof the frames 20 and 21 via the seat plate 31. A rotary shaft 30 a ofthe drive motor 30 penetrates through the seat plate 31 and the firstframe 20 in a horizontal direction, and projects toward the second frame21 at the opposite side. An external gear 32, a gear with the teethformed on its outer surface, is connected to the leading end of therotary shaft 30 a as a single integrated unit. A pitch circle of theexternal gear 32 is relatively small in order to achieve a relativelylarge deceleration ratio.

The first frame 20 and the second frame 21 are connected by a supportshaft 35 disposed horizontally near the drive motor 30. A driveninternal gear 36, a gear with the teeth formed on its inner surface, isrotatably supported by the support shaft 35 to be proximal to theexternal gear 32. The driven internal gear 36 includes an outer cylinderportion 36 a, an inner cylinder portion 36 b, a shaft hole 36 c, and anend plate 36 d.

The outer cylinder portion 36 a, the inner cylinder portion 36 b, andthe shaft hole 36 c are disposed concentrically around the support shaft35. The outer cylinder portion 36 a and the inner cylinder portion 36 bconstitute a concentric double-wall connecting structure, therebyenhancing the durability of the internal gear 36. The end plate 36 d isdisposed opposite the first frame 20, and connects one end of the outercylinder portion 36 a, the inner cylinder portion 36 b, and the shafthole 36 c in the axial direction, thereby sealing one side of theinternal gear 36. As shown in FIG. 1A, the shaft hole 36 c is long inthe axial direction. However, the shaft hole 36 c does not have to belong in the axial direction. Alternatively, the shaft hole 36 c may havesubstantially the same dimension as the thickness of the end plate 36 d.

The other end of the internal gear 36, which is not covered with the endplate 36 d, faces the frame 20 to which the drive motor 30 is attached.An annular opening 37 between the outer cylinder portion 36 a and theinner cylinder portion 36 b faces the frame 20. Internal teeth 36 e areformed on the inner circumferential surface of the outer cylinderportion 36 a. The external gear 32 of the drive motor 30 inserted intothe annular opening 37 meshes with the internal teeth 36 e. Asillustrated in FIG. 1B, the inner cylinder portion 36 b and the shafthole 36 c are connected by ribs 36 f in a radial direction. In theillustrative embodiment, six ribs 36 f are provided. However, the numberof the ribs is not limited to six.

The leading end portion of the external gear 32 is tapered or narrowstoward the leading end (hereinafter referred to as a male taper portion40). A female taper portion 41 is formed on the rim of the opening ofthe outer cylinder portion 36 b. The male taper portion and the femaletaper portion 41 allow the external gear 32 to be inserted into theannular opening 37 and mesh with the internal gear 36 e smoothly.

As illustrated in FIGS. 1A and 1B, an access hole 42 is formed at eachof three positions around the circumference of the end plate 36 d atcertain intervals. The external gear 32 is accessed through the threeaccess holes 42 when supplying grease to the external gear 32 andchecking the gear meshing performance.

As illustrated in FIG. 1A, the first frame 20 at the drive motor sideincludes an annular rib 20 a having a predetermined height. The annularrib 20 a is formed to surround a portion of or an entire circumferenceof the exterior of the outer cylinder portion 36 a at the opening side.The annular rib 20 a overlaps with an outer circumference of the driveninternal gear 36 in the radial direction by a certain amount in theaxial direction. Accordingly, the annular opening 37 of the internalgear 36 is prevented from getting directly exposed to the outside.

An external gear 44 (i.e., a second external gear) is formed integrallyon the outer surface of the end plate 36 d of the driven internal gear36. The outer diameter of the external gear 44 is approximately half theexternal diameter of the driven internal gear 36. The support shaft 35of the driven internal gear 36 penetrates through the shaft center ofthe external gear 44. The driven internal gear 36 and the external gear44 jointly rotate about the support shaft 35.

A driven shaft 45 as a drive target is horizontal and rotatably attachedto the second frame 21 opposite the first frame 20. An input shaft 45 aof the driven shaft 45 is supported by the second frame 21 via a shaftbearing 46. The input shaft 45 a of the driven shaft 45 protrudesbetween the first frame 20 and the second frame 21. An external gear 47is connected to the input shaft 45 a.

The external gear 47 meshes with the external gear 44 integrated withthe driven internal gear 36. Accordingly, the drive force of the drivemotor 30 is transmitted sequentially from the external gear 32, thedriven internal gear 36, the external gear 44, the external gear 47, andthe driven shaft 45.

When the drive force is transmitted from the external gear 32 to theinternal teeth 36 e of the driven internal gear 36, noise and vibrationdue to meshing gears are confined in the annular opening 37. Thestiffness of the driven internal gear 36 is enhanced by the concentricdouble-wall connecting structure constituted of the outer cylinderportion 36 a, the inner cylinder portion 36 b, and the end plate 36 d.With this configuration, noise and vibration are reliably andeffectively prevented from getting dispersed outside the driven internalgear 36. It is to be noted that a transmission path of a subsequentstage (second stage) downstream from the driven internal gear 36includes, in addition to the external gear 47, a second-stage internalgear or a second-stage pulley individually, or arbitrarily combined.

[Embodiment 2]

With reference to FIG. 2, a description is provided of anotherillustrative embodiment of the present disclosure. In the presentillustrative embodiment, the external gear 44 integrally provided withthe drive internal gear 36 in Embodiment 1 is changed to a secondinternal gear 50. Both ends of the support shaft 35 common to the driveninternal gear 36 and the second internal gear 50 are supported by a pairof the first and the second frames 20 and 21. An external gear 51 with arelatively small diameter meshes with internal teeth 50 a of the secondinternal gear 50. The external gear 51 is rotatably supported by asupport shaft 52 integrally formed with the second frame 21.

The external gear 51 is integrated with an external gear 53 having arelatively large diameter. The external gear 53 is disposed outside thesecond internal gear 50. The external gears 51 and 53 constitute thesecond stage of the gear assembly. The external gear 53 of the secondstage meshes with the external gear 47 attached to the input shaft 45 aof the driven shaft 45. Except for the configuration described above,the configurations in the present illustrative embodiment are similar toor the same as in Embodiment 1 shown in FIGS. 1A and 1B. Thus, thedescription thereof is omitted.

[Embodiment 3]

With reference to FIG. 3, a description is provided of anotherillustrative embodiment of the present disclosure. In the presentillustrative embodiment, the drive motor 30 drives simultaneously both atop and a bottom shafts, i.e., a driven shaft 55 and the driven shaft45. In other words, external teeth (second external gear) 50 b areformed on the outer circumferential surface of the second internal gear50. The external teeth 50 b mesh with an external gear 54 attached to aninput shaft 55 a of the driven shaft 55.

The input shaft 55 a is rotatably supported by the second frame 21through a shaft bearing 56. Except for the configuration describedabove, the configurations in the present illustrative embodiment aresimilar to or the same as that shown in FIG. 2. According to the presentillustrative embodiment, the drive torque of the drive motor 30 isdistributed in accordance with a deceleration ratio of gears to thedriven shafts 45 and 55.

[Embodiment 4]

With reference to FIG. 4, a description is provided of anotherillustrative embodiment of the present disclosure. In the presentillustrative embodiment, a driven shaft 60 is disposed perpendicular tothe rotary shaft 30 a of the drive motor 30. In other words, the frame20 to which the drive motor 30 is attached is disposed horizontally, andthe rotary shaft 30 a of the drive motor 30 and the external gear 32 aredisposed facing upward in the vertical direction.

It is to be noted that in Embodiment 1, the driven internal gear 36 andthe external gear 44 are disposed vertically. In the presentillustrative embodiment, by comparison, the driven internal gear 36 andthe external gear 44 are disposed horizontally. Other than that, thedriven internal gear 36 and the external gear 44 have the sameconfigurations as that in Embodiment 1.

In Embodiment 4, the external gear 44 is changed to a bevel gear (secondexternal gear) 44 a. Another bevel gear 61 meshes vertically with thebevel gear 44 a. The bevel gear 61 of the second stage is attached to aninput shaft 60 a of the horizontally-disposed driven shaft 60. The inputshaft 60 a is rotatably supported by a shaft bearing 62 disposed on athird planar frame 22 disposed vertically.

The bevel gear 44 a and the bevel gear 61 may be helical gears and meshwith each other. By meshing the helical gears, the driven internal gear36 is biased in the axial direction due to a force in the axialdirection of the meshing drive torque acting on the helical gears.

As described above, when there is a gap between the driven internal gear36 and the frame 20, noise and vibration easily disperse outside fromthe gap. Generally, the driven internal gear 36 is configured to includesome clearance in the axial direction, thereby facilitating assembly ofthe gears. By biasing the driven internal gear 36 against the frame bythe force of the helical gears, the gap between the frame 20 and thedriven internal gear 36 can be reduced as much as possible. The angulardirection of the helical gear is set such that the driven internal gear36 is biased towards the frame 20.

Both ends of the support shaft 35, which is a common shaft for thedriven internal gear 36 and the bevel gear 44 a, are supported by thepair of the top and the bottom frames 20 and 21. Because the externalgear 32 is disposed vertically facing upward, the annular opening 37 ofthe driven internal gear 36 faces down, thereby preventing foreignsubstance such as dust from entering inside the driven internal gear 36.Furthermore, this configuration facilitates downward application of thegrease to the external gear 32 from the access hole 42 of the end plate36 d of the driven internal gear 36.

[Embodiment 5]

With reference to FIG. 5, a description is provided of anotherillustrative embodiment of the present disclosure. According to thepresent illustrative embodiment, two driven shafts 45 and 65 are drivensimultaneously by the drive motor 30. An external gear 66 (thirdexternal gear) attached to an input shaft 65 a of a second driven shaft65 meshes with the external gear 32. The input shaft 65 a is rotatablysupported by a fourth planar frame 23 via a shaft bearing 67. The fourthplanar frame 23 is perpendicular to the input shaft 65 a. Except for theconfiguration described above, the configurations of Embodiment 5 arebasically the same as Embodiment 1 shown in FIGS. 1A and 1B.

According to the present illustrative embodiment, when constituting thedriven internal gear 36 with a resin gear, in particular, the loadapplied to the resin gear is effectively reduced. In other words, whentransmitting the entire drive torque of the external gear 32 through thedriven internal gear 36, the load is applied to the driven internal gear36 excessively. In view of the above, a part of the drive torque isdistributed to the driven shaft 65 by the external gear 66. It is to benoted that due to the degree of the contact ratio of the gears the drivetorque distributed to the driven internal gear 36 can be set greaterthan the drive torque distributed to the external gear 66.

[Embodiment 6]

With reference to FIG. 6, a description is provided of anotherillustrative embodiment of the present disclosure. According to thepresent illustrative embodiment, three driven shafts 45, 65, and 75 aresimultaneously driven by the drive motor 30. Torque is distributed tothe three driven shafts 45, 65, and 75 in accordance with thedeceleration ratio before the three driven shafts 45, 55, and 75. Thegear train before the first driven shaft 45 and the second driven shaft65 is the same as that of Embodiment 5.

An external gear 76 attached to an input shaft 75 a of a third drivenshaft 75 is driven by the external gear 32 via an external gear 77(third external gear) attached rotatably to the support shaft 35. Inother words, the external gear 77 in the middle meshes with both theexternal gear 32 and the external gear 76, thereby transmitting drivingtorque. It is to be noted that due to the degree of the contact ratio ofthe gears the drive torque distributed to the driven internal gear 36can be set greater than the drive torque distributed to the externalgear 66 or the external gear 77.

[Embodiment 7]

With reference to FIG. 7, a description is provided of anotherillustrative embodiment of the present disclosure. According to thepresent illustrative embodiment, the rotary shaft 30 a of the drivemotor 30 is disposed vertically upward. Two driven shafts 60 and 65, onebeing horizontally disposed and another being vertically disposed, aredriven simultaneously by the drive motor 30. Similar to theconfiguration shown in FIG. 4, the annular opening 37 of the driveninternal gear 36 faces downward, thereby preventing foreign substancesuch as dust from entering inside the driven internal gear 36.

The external gear 66 (third external gear) attached to the input shaft65 a of the second driven shaft 65 meshes with the external gear 32 ofthe drive motor 30 between the driven internal gear 36 and the frame 20.The input shaft 65 a is rotatably supported through the shaft bearing 67by the frame 23 horizontally disposed. The upper end of the supportshaft 35 is supported by an extension 23 a extended from the frame 23.Except for the configuration described above, the configurations in thepresent illustrative embodiments are similar to or the same as thatshown in FIG. 4.

According to the present illustrative embodiment, the external gear 32,the internal teeth 36 e, and the bevel gears 44 a and 61 may havehelical teeth. With this configuration, the driven internal gear 36 canbe biased against the frame 20 at the bottom by the force in the axialdirection of the drive torque.

[Embodiment 8]

With reference to FIG. 8, a description is provided of anotherillustrative embodiment of the present disclosure. In the presentillustrative embodiment, the drive motor 30 drives simultaneously twodriven shafts 45 and 65 which are disposed parallel to each other andspaced apart in the vertical direction. The external gear 66 (thirdexternal gear) attached to the input shaft 65 a of the upper drivenshaft 65 meshes with the external gear 32 of the drive motor 30.

The input shaft 65 a is supported through the shaft bearing 67 by theframe 23 vertically disposed. The outer circumference of the outercylinder portion 36 a of the driven internal gear 36 at the opening sideis covered with a rib 20 b extending from the frame 20 in the horizontaldirection. With this configuration, noise and vibration caused bymeshing the external gear 32 and the internal teeth 36 e are preventedfrom getting dissipated outside. Except for the configuration describedabove, the configurations of the present illustrative embodiment aresimilar to or the same as Embodiment 1 shown in FIGS. 1A and 1B.

[Embodiment 9]

With reference to FIG. 9, a description is provided of anotherillustrative embodiment of the present disclosure. In the presentillustrative embodiment, the drive motor 30 drives simultaneously twodriven shafts 80 and 81 which are closely disposed parallel to eachother in the vertical direction. An input shaft 80 a of the driven shaft80 serves also as a support shaft for the driven internal gear 36 andfor the external gear 77. The input shaft 80 a is rotatably supported bythe frame 21 through a shaft bearing 84.

An input shaft 81 a of the driven shaft 81 at the bottom is rotatablysupported by the second frame 21 through a shaft bearing 82. The otherend or the leading end of the input shaft 81 a extends towards the firstframe 20 at the opposite side and is rotatably supported by the firstframe 20. An external gear 83, which is a tenth gear at the driven side,is attached to the input shaft 81 a near the leading end thereofrotatably supported by the first frame 20. The external gear 83 mesheswith the external gear 77 (third external gear) in the middle. Theexternal gear 77 in the middle meshes with both the external gear 32 andthe external gear 83 (tenth gear) of the driven side.

As illustrated in FIG. 9, the external gear 32 of the drive motor 30 iscovered with a rib 20 c projecting horizontally from the upper portionof the frame 20. With this configuration, noise and vibration due tomeshing gears, i.e., the external gear 32 and the internal teeth 36 e,are confined inside the driven internal gear 36.

[Embodiment 10]

With reference to FIG. 10, a description is provided of anotherillustrative embodiment of the present disclosure. In the presentillustrative embodiment, the drive motor 30 drives simultaneously twodriven shafts 45 and 81 which are disposed parallel to each other andspaced apart in the vertical direction. The driving method for the lowerdriven shaft, i.e., the driven shaft 81, is the same as that of FIG. 9.

The driving method for the upper driven shaft, i.e., the driven shaft45, is the same as that of Embodiment 2 and Embodiment 3 shown in FIGS.2 and 3. More specifically, the driven shaft 45 is driven by the outputof the external teeth 50 a of the second internal gear 50 having aslightly smaller diameter than that of the driven internal gear 36. Thedriven internal gear 36 and the second internal gear 50 are disposedback-to-back as an integrated unit.

The support shaft 52 is attached to the second frame 21. The two-stageexternal gear including the external gear 51 with a large diameter andthe external gear 53 with a small diameter is attached rotatably to thesupport shaft 52. The external gear 51 with a small diameter meshes withthe internal teeth 50 a. The external gear 53 with a large diametermeshes with the external gear 47 attached to the input shaft 45 a of thesecond driven shaft 45. With this configuration, the rotation of thesecond internal gear 50 is decelerated, and the decelerated rotation istransmitted to the driven shaft 45.

[Embodiment 11]

With reference to FIG. 11, a description is provided of anotherillustrative embodiment of the present disclosure. In the presentillustrative embodiment, the drive motor 30 drives simultaneously twodriven shafts 55 and 81 which are disposed parallel to each other andspaced apart in the vertical direction. The driving method for the lowerdriven shaft, i.e., the driven shaft 81, is the same as that ofEmbodiment 9 and Embodiment shown in FIGS. 9 and 10, respectively.

The upper driven shaft, i.e., the driven shaft 55, is driven by theexternal gear 54. More specifically, the driven internal gear 36 and theexternal gear (second external gear) 44 are disposed back-to-back as anintegrated unit. The external gear 54 attached to the input shaft 55 aof the second driven shaft 55 meshes with the external gear 44. Theinput shaft 55 a is rotatably supported by the second frame 21 throughthe shaft bearing 56.

[Embodiment 12]

With reference to FIG. 12, a description is provided of anotherillustrative embodiment of the present disclosure. In the presentillustrative embodiment, the drive motor 30 drives simultaneously threedriven shafts 45, 81, and 86 which are disposed horizontally andparallel to each other. The driving method for the top and the bottomdriven shafts, i.e., the driven shafts 45 and 81, respectively, is thesame as that of Embodiment 10 shown in FIG. 10.

An external gear 87 with a relatively small diameter attached to aninput shaft 86 a of a third driven shaft 86 in the middle meshes withthe external teeth 50 b formed on the outer circumferential surface ofthe second internal gear 50, thereby driving the third driven shaft 86.The third driven shaft 86 and the second internal gear 50 are formedback-to-back as an integrated unit. The input shaft 86 a is rotatablysupported by the second frame 21 through a shaft bearing 88.

[Embodiment 13]

With reference to FIG. 13, a description is provided of anotherillustrative embodiment of the present disclosure. According to thepresent illustrative embodiment, two driven shafts 60 and 65, one beingvertically disposed and another being horizontally disposed, are drivensimultaneously by the drive motor 30. In FIG. 13, the external gear 32is disposed vertically upward. Two frames 20 and 21 are disposedhorizontally. FIG. 13 shows the gear assembly of FIG. 7 with left andright reversed. In order to drive the perpendicular second driven shaft65, rather than obtaining a drive torque directly from the external gear32 of the drive motor 30, an external gear (third external gear) 89 isdisposed substantially in the middle.

The external gear 89 is rotatably supported by the support shaft 35 ofthe driven internal gear 36, while meshing with the external gear 32 ofthe drive motor 30 at one side and meshing with the external gear 66attached to the input shaft 65 a of the driven shaft 65 on the otherside. Except for the configuration described above, the configuration ofEmbodiment 13 is basically the same as that of Embodiment 7 shown inFIG. 7.

It is to be noted that due to the degree of the contact ratio of thegears the drive torque distributed to the driven internal gear 36 can beset greater than the drive torque distributed to the external gear 86.

The gear transmission device according to the illustrative embodimentsis applied to various devices to drive a target. For example, the geartransmission device is applicable to an image forming apparatus.

With reference to FIG. 14, a description is provided of an image formingapparatus employing the gear transmission device according to theillustrative embodiments of the present disclosure. FIG. 14 is aperspective view schematically illustrating a laser printer as anexample of the image forming apparatus. In the image forming apparatus,the gear transmission device of the illustrative embodiments describedabove drives at least one of process units 1K, 1Y, 1M, and 1C, imagebearing members 2K, 2Y, 2M, and 2C, an intermediate transfer belt 16, asheet feed roller 130 a, and a fixing device 134.

As illustrated in FIG. 14, the image forming apparatus includes a sheettray 130 at the bottom thereof. A lateral cover 8, which can be openedupon inspection of the inside of the image forming apparatus, isdisposed above the sheet tray 130 and constitutes an exterior surface ofthe image forming apparatus. A sheet output tray 144 is disposed at theupper portion of the image forming apparatus. Inside the lateral cover8, a duplexing unit 9 is disposed. A rotary shaft 12 is disposed at thebottom of the image forming apparatus, and the lateral cover 8 isrotatable about the rotary shaft 12 towards the front.

The duplexing 9 unit includes a conveyor housing. At the back of theconveyor housing, a sheet return path is formed. The inner side of theconveyor housing constitutes a portion of the sheet delivery path in themain body of the image forming apparatus. A secondary transfer roller120 serving as a transfer device and one of the timing rollers 132, thatis, a drive roller, are disposed at the inner side of the conveyorhousing. As will be described later, the secondary transfer roller 120and a drive roller 18 at the main body side constitute a roller pairthat delivers the recording medium P. The secondary transfer roller anda drive roller at the main body side constitute the timing roller pair132.

As illustrated in FIG. 14, the image forming apparatus includes a mainbody housing in which four process units 1K, 1Y, 1M, and 1C, one foreach of the primary colors black, yellow, magenta, and cyan,respectively, are disposed. The process units 1K, 1Y, 1M, and 1C serveas image forming units that form images using developing agents ofblack, yellow, magenta, and cyan. It is to be noted that the suffixes K,Y, M, and C denote colors black, yellow, magenta, and cyan,respectively, and these suffixes are omitted, unless discrimination ofthe colors is necessary.

The process units 1K, 1Y, 1M, and 1C includes toner bottles 6K, 6Y, 6M,and 6C that store unused toner of black, yellow, magenta, and cyan,respectively. The process units 1K, 1Y, 1M, and 1C all have the sameconfiguration as all the others, differing only in the color of toneremployed. Thus, a description is provided of the process unit 1K as anexample of the process units. As illustrated in FIG. 14, the processunit 1K for forming a black toner image includes a drum-shaped imagebearing member (i.e., photosensitive drum) 2K serving as a latent imagebearing member, a charging device 4K, a developing device 5K, a drumcleaning device 3K, a charge neutralizer, and so forth. The process unit1K is detachably attachable relative to the main body housing of theimage forming apparatus, thereby allowing consumables in the processunit 1K to be replaced at once.

An exposure device 7 is disposed above the process units 1K, 1Y, 1M, and1C. The exposure device 7 includes a light source such as a laser diodeto project laser light based on image data.

A transfer unit 15 serving as a primary transfer unit is disposed belowthe process units 1K, 1Y, 1M, and 1C. The transfer unit 15 includes fourprimary transfer rollers 19K, 19Y, 19M, and 19C, the intermediatetransfer belt 16, the drive roller 18, a driven roller 17, the secondarytransfer roller 120, a belt cleaning device 121, a cleaning auxiliaryroller 122, and so forth. The primary transfer rollers 19K, 19Y, 19M,and 19C face the image bearing members 2K, 2Y, 2M, and 2C, respectively,via the intermediate transfer belt 16. The intermediate transfer belt 16is formed into an endless loop and entrained around the drive roller 18and the driven roller 17. The intermediate transfer belt 16 is moved ina predetermined direction. The secondary transfer roller 120 is disposedfacing the drive roller 18 and serves as a secondary transfer device.The image bearing members 2K, 2Y, 2M, and 2C serve as first imagebearing members. The intermediate transfer belt 16 serves as a secondimage bearing member on which a composite image is transferred.

The sheet tray 130 and the sheet feed roller 130 a are disposedsubstantially at the bottom of the image forming apparatus. The sheettray 130 stores a plurality of recording media P. The sheet feed roller130 a picks up and sends a recording medium P from the sheet tray 130 toa sheet path 131. A pair of timing rollers 132 is disposed near the endof the sheet path 131. The pair of timing rollers 132 stops temporarilythe recording medium.

The pair of the timing rollers 132 is disposed near the intermediatetransfer belt 16 at the upstream side in the conveyance direction of therecording medium P. The pair of the timing rollers 132 stops temporarilythe recording medium P so as to align with a toner image on theintermediate transfer belt 16. Immediately before transferring the tonerimage formed on the intermediate transfer belt 16 to the recordingmedium P in a secondary transfer nip defined by the drive roller 18 andthe secondary transfer roller 120 via the intermediate transfer belt 16,the pair of the timing rollers 132 rotates again to feed the recordingmedium P to the secondary nip at a predetermined timing.

Sheet conveyor rollers herein refer to rollers associated withconveyance of the recording medium P. The sheet conveyor rollersinclude, but are not limited to the sheet feed roller 130 a, a timingdrive roller, a pair of sheet output rollers 137, and a pair of sheetreverse conveyor rollers 143.

Substantially above the secondary transfer nip between the secondarytransfer roller 120 and the drive roller 18, a post-transfer sheet path133 is provided. Substantially near the end of the post-transfer sheetpath 133, the fixing device 134 serving as a fixing section is disposed.The fixing device 134 includes a fixing roller 134 a and a pressingroller 134 b. The fixing roller 134 a includes a heat source such as ahalogen lamp inside thereof. While rotating, the pressing roller 134 bpressingly contacts the fixing roller 134 a at a predetermined pressure,thereby forming a heated area called a fixing nip therebetween.

A post-fixing sheet path 135 is provided above the fixing device 134. Atthe end of the post-fixing sheet path 135, the post-fixing sheet path135 splits into a sheet output path 136 and a reverse conveyor path 141.A switching member 142 that swingably rotates about a shaft 142 a isdisposed at the post-fixing sheet path side. The pair of sheet outputrollers 137 is disposed at the end of the sheet output path 136. The endof the reverse conveyor path 141 joins the sheet feed path 131. The pairof reverse conveyor rollers 143 is disposed on the reverse conveyor path141. The sheet output tray 144 is disposed at the upper portion of theimage forming apparatus. The sheet output tray 144 is formed by curvinga top cover of the image forming apparatus inward.

A powder storage (toner storage) 10 for storing waste toner is disposedbetween the transfer device 15 and the sheet tray 130. The powdercontainer 10 is detachably attachable relative to the main body housingof the image forming apparatus.

In the image forming apparatus of the present illustrative embodiment,the sheet feed roller 130 a and the secondary transfer roller 120 needto be spaced apart due to conveyance of the recording medium P. Such anempty space is used to accommodate the powder container 10, therebymaking the image forming apparatus as a whole as compact as is usuallydesired.

Still referring to FIG. 14, a description is provided of a basic imageforming operation performed by the image forming apparatus of thepresent illustrative embodiment. In FIG. 14, as the sheet feed roller130 a is rotated based on a sheet feeding signal from a controller ofthe image forming apparatus, the top sheet of the recording mediastacked on the sheet tray 130 is separated and fed to the sheet path131. As the leading end of the recording medium P reaches a nip portiondefined by the pair of the timing rollers 132, rotation of the pair ofthe timing rollers 132 is stopped temporarily so as to align therecording medium P with the toner image formed on the intermediatetransfer belt 16 and to correct skew of the leading end of the recordingmedium P.

A description is provided of the image forming operation of the processunit 1K as an example of the image forming operation of the processunits. Initially, the surface of the image bearing member 2K isuniformly charged at a high electrical potential by the charging device4K. The exposure device 7 illuminates the image bearing member 2K with alaser beam L based on image data. As a result, the electrical potentialof the illuminated portion of the image bearing member 2K drops, therebyforming an electrostatic latent image on the surface of the imagebearing member 2K. Fresh (unused) black toner is supplied to thedeveloping device 5K from the toner bottle 6K.

Subsequently, the electrostatic latent image formed on the image bearingmember 2K is supplied with the black toner by the developing device 5K,and the black toner image is formed on the image bearing member 2K.Then, the black toner image on the image bearing member 2K istransferred onto the intermediate transfer belt 16 in an intermediatetransfer process.

The drum cleaning device 3K removes residual toner remaining on thesurface of the photosensitive drum 2K after the intermediate transferprocess. The removed residual toner is transported to a waste tonercontainer in the process unit 1K by a waste toner conveyor. The chargeneutralizer removes residual charge remaining on the image bearingmember 2K after cleaning.

Similar to the image forming operation in the process unit 1K, in theprocess unit 1Y, 1M, and 1C, toner images are formed on the imagebearing members 2Y, 2M, and 2C, and each of the toner images istransferred onto the intermediate transfer belt 16 such that they aresuperimposed on top of the black toner image which has been transferredon the intermediate transfer belt 16, thereby forming a composite tonerimage on the intermediate transfer belt 16.

As the toner images are transferred onto the intermediate transfer belt16 one atop the other, rotation of the pair of timing rollers 132 andthe sheet feed roller 130 a is initialized to send the recording mediumP to the secondary transfer roller 120 in appropriate timing such thatthe recording medium P is aligned with the composite toner image formedon the intermediate transfer belt 16. Subsequently, at the secondarytransfer nip between the secondary transfer roller 120 and theintermediate transfer belt 16, the toner image formed on theintermediate transfer belt 16 is transferred onto the recording medium Pin a process known as a secondary transfer process, thereby forming animage on the recording medium P.

After the composite toner image is transferred onto the recording mediumP, the recording medium P is transported, via the post-transfer sheetpath 133, to the fixing device 134 in which heat and pressure areapplied to the recording medium P, thereby fixing the composite tonerimage on the recording medium P. More specifically, the recording mediumP bearing an unfixed toner image on the surface thereof is delivered tothe fixing device 134 and interposed between a fixing roller 134 a and apressing roller 134 b in the fixing device 134. Heat and pressure areapplied to the unfixed toner image on the recording medium P, therebyfusing and fixing the toner image on the recording medium P. After thecomposite toner image is fixed on the recording medium P, the recordingmedium P is delivered from the fixing device 134 to the post-fixingsheet path 135.

It is to be noted that when the recording medium P is discharged fromthe fixing device 134, the switching member 142 is at the positionindicated by a solid line in FIG. 14. In this state, the place near theend of the post-fixing sheet path 135 is opened. After the recordingmedium P is discharged from the fixing device 134, the recording mediumP is delivered along the post-fixing sheet path 135 to the pair of thesheet output rollers 137 and discharged onto the sheet output tray 144.

For double sided printing, after the rear end of the recording medium Pconveyed by the pair of sheet output rollers 137 passes through thepost-fixing sheet path 135, the switching member 142 moves to a positionindicated by a broken line in FIG. 14 to close the sheet path near theend of the post-fixing sheet path 135. Substantially at the same time,the pair of sheet output rollers 137 starts to rotate in the oppositedirection, thereby transporting the recording medium P in the oppositedirection and allowing the recording medium P to enter the reverseconveyor path 141.

The recording medium P conveyed along the reverse conveyor path 141passes through the pair of reverse conveyor rollers 143 and arrives atthe pair of the timing rollers 132. Subsequently, the pair of the timingrollers 132 stops the recording medium P temporarily and sends therecording medium P again in appropriate timing such that the recordingmedium P is aligned with the toner image for the second side (backsurface) formed on the intermediate transfer belt 16. As the recordingmedium P passes through the secondary transfer roller 120, the tonerimage is transferred onto the second side of the recording medium P.

After the toner image on the second side of the recording medium P isfixed thereon by the fixing device 134, the recording medium P isdischarged from the fixing device 134 and delivered to the sheet outputtray 144 through the post-fixing sheet path 135, the sheet output path136, and the pair of the sheet output rollers 137, accordingly.

After the toner image on the intermediate transfer belt 16 istransferred onto the recording medium P, residual toner not having beentransferred onto the recording medium P is adhered to the intermediatetransfer belt 16. The residual toner is removed from the intermediatetransfer belt 16 by a belt cleaning device 121.

The toner removed from the intermediate transfer belt 16 is delivered tothe powder container 10 by the waste toner conveyor and collected in thepowder container 10.

In a case in which paper jams occur during printing, users may manuallyopen the lateral cover 8 which rotates about the shaft 12 and remove thejammed paper from inside. In a case in which the recording medium P iscaught between the pair of timing rollers 132, it is difficult to removethe recording medium P from the timing rollers 132 while the timingrollers 132 press against each other at a high pressure.

According to the present illustrative embodiment, the transfer roller120 and one of the timing rollers 132, that is, the drive roller, aredisposed inside the lateral cover 8. With this configuration, as thelateral cover 8 is opened, the transfer roller 120 and the pair oftiming rollers 132 can be separated at the same time, therebyfacilitating removal of the jammed paper quickly. More specifically,moving the lateral cover 8 about the shaft 12 towards the front allowsthe fixing device 134, the end portion of the intermediate transfer belt16, the driven roller, and so forth to be visible, hence facilitatingremoval of the jammed paper.

The gear transmission device may further include a transmission deviceequipped with a downstream external gear, a downstream internal gear,and a downstream pulley. The downstream external gear, the downstreaminternal gear, and the downstream pulley are disposed alone or incombination on a transmission path downstream from one of the firstexternal gear and from the first internal gear.

According to an aspect of this disclosure, the present invention isemployed in the image forming apparatus. The image forming apparatusincludes, but is not limited to, an electrophotographic image formingapparatus, a copier, a printer, a facsimile machine, and amulti-functional system.

Furthermore, it is to be understood that elements and/or features ofdifferent illustrative embodiments may be combined with each otherand/or substituted for each other within the scope of this disclosureand appended claims. In addition, the number of constituent elements,locations, shapes and so forth of the constituent elements are notlimited to any of the structure for performing the methodologyillustrated in the drawings.

Example embodiments being thus described, it will be obvious that thesame may be varied in many ways. Such exemplary variations are not to beregarded as a departure from the scope of the present invention, and allsuch modifications as would be obvious to one skilled in the art areintended to be included within the scope of the following claims.

What is claimed is:
 1. A power transmission device, comprising: a firstframe; a drive motor including a rotary shaft attached to a first sideof the first frame, the rotary shaft including first external teeth onan outer circumferential surface of the rotary shaft; a first drivenrotatable gear near the rotary shaft, the first driven rotatable gearincluding an annular concave portion including an internal teeth portionon an inner circumferential surface of the annular concave portion; asecond driven rotatable gear near the rotary shaft, the second drivenrotatable gear including second external teeth on an outercircumferential surface thereof; wherein when the annular concaveportion faces the first frame, the first external teeth of the rotaryshaft are configured to be inserted into the annular concave portion soas to engage directly the first external teeth and the internal teeth,and the second external teeth are configured to engage the firstexternal teeth which are not in mesh with the first driven rotatablegear.
 2. The power transmission device according to claim 1, furthercomprising: a third driven rotatable gear near the rotary shaft, thethird driven rotatable gear including third external teeth on an outercircumferential surface of the third driven rotatable gear, wherein thethird external teeth is configured to engage the first external teethwhich are not in mesh with the first driven rotatable gear and thesecond driven rotatable gear.
 3. The power transmission device accordingto claim 1, wherein the second driven rotatable gear is configured totransmit power from the drive motor to an image bearing member.
 4. Thepower transmission device according to claim 1, wherein a side of thefirst frame facing the annular concave portion includes an annular ribconfigured to surround at least a portion of an outer circumference ofthe first driven rotatable gear.
 5. The power transmission deviceaccording to claim 1, wherein the first driven rotatable gear is adeceleration gear.
 6. The power transmission device according to claim1, further comprising: an external gear on an end portion of the firstdriven rotatable gear opposite the drive motor as a single integratedmember.
 7. The power transmission device according to claim 6, wherein adiameter of the external gear is smaller than that of the internal teethportion of the first driven rotatable gear.
 8. The power transmissiondevice according to claim 1, wherein the first external teeth of therotary shaft and the internal teeth portion of the first drivenrotatable gear include helical gears, and an angular direction of thehelical gears is set such that a drive torque acting on the helicalgears biases the first driven rotatable gear towards the side of theframe facing the annular concave portion.
 9. The power transmissiondevice according to claim 1, further comprising: a second frame facingthe first frame, wherein the first driven rotatable gear is between thefirst frame and the second frame, and each end of a support shaft thatis configured to rotatably support the first driven rotatable gear issupported by the first frame and the second frame.
 10. The powertransmission device according to claim 1, wherein an end portion of thefirst driven rotatable gear opposite the drive motor includes a holethat is configured to allow access to the rotary shaft.
 11. An imageforming apparatus, comprising: the power transmission device of claim 1.